1. Field of Invention
This invention relates to acid digestion and simultaneous catalytic chemical conversion of cellulose materials to ethanol at greater than 90 percent yields, in less than 5 minutes, in a single process step. Specifically cellulosic materials, comprising newspaper, wood sawdust, corn cobs, switchgrass and bagasse, are catalytically converted to ethanol using a soluble catalyst in a sulfuric acid medium in the absence of nitrogen and phosphorous compounds, in air at 110° C. to 180° C. employing catalysts based on transition metal complexes possessing a degree of symmetry as described herein.
2. Description of Prior Art
The chemical process industry has grown to maturity based on petroleum feed stocks, a non-renewable resource, that may become unavailable in the next 80 years. This planet Earth fosters continual growth of abundant carbohydrate based plants including fruits, vegetables, starches, grain food sources, grasses, cotton, shrubs, trees and related natural cellulosic materials. Grains, corn cobs, bagasse, support plant stalks and grasses are, in part, subject to bio-fermentation processes producing ethanol and related products at modest yields. These processes are slow and may convert some ten percent of the cellulose and related materials to ethanol.
Direct Catalytic Conversion of Cellulosic Materials to Ethanol, the subject of this application, teaches conversion efficiencies of at least 90 percent in less than 5 minutes. This process affords complete use of renewable plant materials, the edible portion for human consumption as food and the residual cellulosic materials for conversion to fuels and industrial chemicals leaving no waste.
A number of process paths have previously been taught for chemical conversion of cellulose and hemi-cellulose materials to ethanol. These processes include fermentation of grain and corn, and dilute acid pre-treatment or acidic steam treatment of dried plant materials followed by fermentation of the resulting sugars. They also include enzymatic digestion of cellulose to hemicelluloses and sugars for fermentation as well as gasification of wood chips to carbon monoxide and hydrogen (synthesis gas) to produce products by Fischer-Tropsch type processes. Gasification is expensive and requires some 300° C. to 600° C. in an inert gas environment. Acidic steam treatment subjects bio-mass to pressure with temperatures up to 180° C. Acid digestion or hydrolysis can be conducted at temperatures of 20° C. to 120° C. while fermentation may be operated in the 20° C. to 55° C. range but is usually limited to conversion rates of less than 20 percent.
Ethanol has been made from ethylene gas dissolved in sulfuric acid then diluted and isolated by distillation. It has also been produced by heating ethylene with steam at 300° C. and 1000 to 4000 psi pressure using acid or acidic transition metal oxide catalysts.
U.S. Pat. No. 8,574,368, issued Nov. 5, 2013, teaches a process for preparation of water-soluble cellulose hydrolysis products in an ionic liquid below 150° C., the cations containing a nitrogen or phosphorus atom. U.S. Pat. No. 8,455,705, issued Jun. 4, 2013, describes a method for catalytic hydrogenation of C4+ water soluble oxygenated biomass-derived hydrocarbons in an aqueous liquid or vapor phase using supported (insoluble) catalysts of Re, Cu, Fe, Ru, Pt, Pd, Ni, W, Mo, Ag, Sn at 100° C. to 400° C. and pressure of 72 psig to 1300 psig. U.S. Pat. No. 7,816,568, issued Oct. 19, 2010, disclosed a process for catalytic conversion of cellulose to ethanol in an acid medium above 200° C. U.S. Pat. No. 7,198,925, issued Apr. 3, 2007, taught steam pretreatment of bale quantities of cereal straw, corn stover or grass for hydrolysis of hemicellulose to xylose at 160° C. to 280° C. U.S. Pat. No. 6,747,067, issued Jun. 8, 2004, described a method for gasification of cellulose to carbon monoxide and hydrogen for subsequent formation of methanol and decomposition products. U.S. Pat. No. 6,660,506, issued Dec. 9, 2003, disclosed a process for dilute acid hydrolysis with metal salts converting cellulose to sugars.
There are a number of dilute acid digestion or pre-treatment process disclosed for partial conversion of cellulose to sugars for subsequent formation of ethanol by fermentation, a biological process. Reported conversions were not higher than 65 percent efficiency and were further limited by fermentation conversions to ethanol of less than 20 percent. U.S. Pat. No. 6,660,506, issued Dec. 9, 2003, teaches dilute acid hydrolysis of cellulose, with metal salts, for such partial conversion to sugars.
The present application discloses non-biological use of low valent transition metal catalysts dissolved in an acid medium saturated with inorganic salts, as described in this application, for direct production of greater than 90 percent yields of ethanol from cellulose materials in less than 5 minutes at ambient pressure.